"We know that the explosively formed penetrators are manufactured in Iran," Pace told Voice of America during a trip to Australia about what senior military officials call EFPs.

"What I would not say is that the Iranian government per se knows about this. It is clear that Iranians are involved and it is clear that materials from Iran are involved, but I would not say, based on what I know, that the Iranian government clearly knows or is complicit," Pace said. (Watch other commanders left out of the loop)

Senior military officials said Sunday that EFPs, which can punch holes in armored vehicles, are made in such a way that they can be traced to Iran.

White House spokesman Tony Snow on Tuesday portrayed the general's comments as in line with the administration's viewpoint.

"He says they exist, correct?" he asked CNN's Ed Henry, who had questioned whether the administration was speaking with one voice. "There are Iranians in Iraq. There's no question about that, correct? So, where's the credibility problem?"

Henry pointed out that Pace was questioning the Iranian government's putative role in the weapons, not the fact that the weapons may have been made in Iran.

The U.S. military has said the munitions are being provided to Shiite groups in Iraq by the Iranian Revolutionary Guard's Quds force, which answers directly to Iranian Supreme Leader Ayatollah Ali Khamenei.

The military officials said a senior operations officer for the Quds force was among several Iranian officers arrested in Irbil -- in Iraq's Kurdish region -- in the past few weeks.

Political maneuvering also alleged

According to the U.S. military, other Iranian officers have provided information that Iran is arming a prominent Iraqi political organization.

Those officers were detained during a December raid on the Baghdad compound of Abdul Aziz Hakim, the head of the Supreme Council for the Islamic Revolution in Iraq, a powerful Shiite political group with close ties to Iran, the U.S. military said.

The Baghdad raid also netted documents that confirmed the arms sale, the U.S. military said.

Officials with the political organization said the munitions were used for security purposes, an assertion disputed by U.S. military officials, who said the mortars and sniper rifles were not intended to be used for self-defense.

The purported credibility problem alluded to by Snow was deepened for some by the fact that the senior military officials who presented their evidence on Sunday did so anonymously and off camera.

"I get a little skeptical about that kind of information," Democratic Sen. Christopher Dodd, a 2008 presidential hopeful, told CNN on Tuesday.

Snow dismissed that concern as unfounded. He added that he had just spoken by telephone with Pace, who told him he and White House officials are on the same page.

Pace was en route back to the United States and unavailable to reporters.

His comments came a day after an official with the Iranian Embassy in Baghdad rejected the administration's assertions of Iranian involvement in Iraq.

"It's all lies and it's not true at all," Iranian Foreign Ministry spokesman Mohammad Ali Hosseini told CNN. "The American administration has made many mistakes in Iraq and now they want to use Iran as a scapegoat."

Senators see echoes of Iraq run-up

In an interview Friday with National Public Radio, Iranian Ambassador to the U.N. Javad Zarif said Iran has provided no weapons to Iraqi insurgents and does not want to.

In the United States, some Iraq war critics likened the Bush administration's highlighting of Iranian involvement in Iraq to the administration's run-up to the war in Iraq, contending officials are attempting a find a reason to invade Iran. The administration denies this.

In an interview on Monday with C-SPAN, Bush said the United States is committed to resolving the impasse over Iran's nuclear program diplomatically.

"We've got a comprehensive policy aimed to solve this peacefully," he said.

Sen. Ron Wyden, an Oregon Democrat, was not persuaded.

"That was said repeatedly before the effort was made to go to war with Iraq," said Wyden.

Wyden, a member of the Senate Intelligence Committee, said Bush administration officials have promised -- and postponed -- a briefing for lawmakers on Iranian links to the Shiite militias blamed for attacks on U.S. troops and the country's Sunni population.

"I want the administration to deliver the full briefing that they promised, the one that's been put off time and time again now, so we can really get at the facts," he said.

Senate Majority Leader Harry Reid told reporters Tuesday that the evidence of Iranian government involvement in Iraq was "very, very weak," adding, "If they are involved, let's see the facts."